/*
 * Copyright (c) 1996, 1999, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */
package java.rmi.dgc;

import java.rmi.*;
import java.rmi.server.ObjID;

/**
 * The DGC abstraction is used for the server side of the distributed
 * garbage collection algorithm. This interface contains the two
 * methods: dirty and clean. A dirty call is made when a remote
 * reference is unmarshaled in a client (the client is indicated by
 * its VMID). A corresponding clean call is made when no more
 * references to the remote reference exist in the client. A failed
 * dirty call must schedule a strong clean call so that the call's
 * sequence number can be retained in order to detect future calls
 * received out of order by the distributed garbage collector.
 *
 * A reference to a remote object is leased for a period of time by
 * the client holding the reference. The lease period starts when the
 * dirty call is received. It is the client's responsibility to renew
 * the leases, by making additional dirty calls, on the remote
 * references it holds before such leases expire. If the client does
 * not renew the lease before it expires, the distributed garbage
 * collector assumes that the remote object is no longer referenced by
 * that client.
 *
 * @author Ann Wollrath
 */
public interface DGC extends Remote {

  /**
   * The dirty call requests leases for the remote object references
   * associated with the object identifiers contained in the array
   * 'ids'. The 'lease' contains a client's unique VM identifier (VMID)
   * and a requested lease period. For each remote object exported
   * in the local VM, the garbage collector maintains a reference
   * list-a list of clients that hold references to it. If the lease
   * is granted, the garbage collector adds the client's VMID to the
   * reference list for each remote object indicated in 'ids'. The
   * 'sequenceNum' parameter is a sequence number that is used to
   * detect and discard late calls to the garbage collector. The
   * sequence number should always increase for each subsequent call
   * to the garbage collector.
   *
   * Some clients are unable to generate a VMID, since a VMID is a
   * universally unique identifier that contains a host address
   * which some clients are unable to obtain due to security
   * restrictions. In this case, a client can use a VMID of null,
   * and the distributed garbage collector will assign a VMID for
   * the client.
   *
   * The dirty call returns a Lease object that contains the VMID
   * used and the lease period granted for the remote references (a
   * server may decide to grant a smaller lease period than the
   * client requests). A client must use the VMID the garbage
   * collector uses in order to make corresponding clean calls when
   * the client drops remote object references.
   *
   * A client VM need only make one initial dirty call for each
   * remote reference referenced in the VM (even if it has multiple
   * references to the same remote object). The client must also
   * make a dirty call to renew leases on remote references before
   * such leases expire. When the client no longer has any
   * references to a specific remote object, it must schedule a
   * clean call for the object ID associated with the reference.
   *
   * @param ids IDs of objects to mark as referenced by calling client
   * @param sequenceNum sequence number
   * @param lease requested lease
   * @return granted lease
   * @throws RemoteException if dirty call fails
   */
  Lease dirty(ObjID[] ids, long sequenceNum, Lease lease)
      throws RemoteException;

  /**
   * The clean call removes the 'vmid' from the reference list of
   * each remote object indicated in 'id's.  The sequence number is
   * used to detect late clean calls.  If the argument 'strong' is
   * true, then the clean call is a result of a failed dirty call,
   * thus the sequence number for the client 'vmid' needs to be
   * remembered.
   *
   * @param ids IDs of objects to mark as unreferenced by calling client
   * @param sequenceNum sequence number
   * @param vmid client VMID
   * @param strong make 'strong' clean call
   * @throws RemoteException if clean call fails
   */
  void clean(ObjID[] ids, long sequenceNum, VMID vmid, boolean strong)
      throws RemoteException;
}
